Table 3.

Results of subgroups analyses

Groups	Categories	Number of studies	Effect estimate	P	Heterogeneity with groups (I2)	Pheterogeneity
Location	North America	7	0.47 (0.33, 0.68)	< 0.001	53%	0.040
	Europe	5	0.47 (0.18, 1.22)	0.120	89%	< 0.001
Follow-up period	≤ 5 years	2	0.65 (0.50, 0.84)	0.001	4%	0.310
	> 5 years	4	0.48 (0.17, 1.31)	0.150	71%	0.020
Study design	Case control	6	0.55 (0.25, 1.20)	0.130	87%	< 0.001
	Cohort	6	0.55 (0.44, 0.69)	< 0.001	36%	0.160
Sample size	≤ 1000	5	0.32 (0.11, 0.88)	0.030	83%	< 0.001
	> 1000	7	0.57 (0.39, 0.82)	0.003	69%	0.003
Adjusted confounders	Multivariable-adjusted	10	0.46 (0.30, 0.71)	< 0.001	81%	< 0.001
	Age-gender adjusted	2	0.09 (0.05, 0.17)	< 0.001	0%	0.340
	Unadjusted	7	0.57 (0.41, 0.81)	0.002	59%	0.020
Quality assessment	High	6	0.59 (0.47–0.74)	< 0.001	31%	0.200
	Moderate	4	0.62 (0.18–2.14)	0.440	91%	< 0.001